The recent advances in plant molecular biology have made possible genetic engineering of most crop species. The technology has been applied to improving agronomic traits, producing pharmaceutical protein, and modifying the final storage products.
The essential parts of plant genetic engineering techniques are promoters that regulate the expression of newly introduced genes. Promoters are genomic fragments that are usually preceding the coding regions of genes and contain regulatory elements recognized by transcription factors of the plant cells. The specific interaction of regulatory elements in promoter region and transcription factors in the cells results in the switch-on and -off of gene transcription.
In general, gene expression is monitored by the comprehensive mechanism which includes multi-levels of the integrative controls, such as transcription, RNA processing, translation and protein processing. However, the majority of genes, especially tissue-specific genes, are mainly regulated at the transcriptional level. Precise control of the tissue-specific genes at transcriptional level in time and space is a prerequisite of cell division and cell differentiation. Therefore, isolation and characterization of the upstream regulatory region of a gene—the promoter are important not only in genetic engineering of plant traits, but also in understanding basic mechanism of cell division and differentiation, which are basis of plant growth and development.
As an important oilseed crop, flax is an excellent target for fixture genetic engineering in efforts to improve agronomic performance, modify fatty acid composition of the seed oil or produce recombinant proteins. Unfortunately, there has been little effort in identification of tissue-specific promoters in flax. In flax, two homologous promoters have been isolated by the PCR cloning strategy, both being the upstream regions of stearoyl-acyl carrier protein desaturase (SAD) genes. The expression pattern of the SAD2 promoter in flax can be regarded as constitutive as it is expressed in most of the tissues. SAD1, on the other hand, is expressed only in roots and seeds, but at the significantly lower level.